Plant now in pots 1/8" deep and seal into sealed zip lock plastic bags. These take at least 6 months to 1 year to germinate. I set mine in my dark basement and check weekly after 5 months. When germination takes place, I remove the bag and usually over winter these seedlings for 1 year indoors before planting outside. A well lit window is all the seedlings need once germinated. Some weak liquid fertilizer also helps build stronger plants.
Clematis are not the easiest of seeds to grow outdoors, and this is why most experts choose to grow theirs in good, measured conditions. A clematis can take 3-5 years to become descent sized.
Suzy